Target seeking missile



N. H. FISK 3,111,088

'Nov. 19, 1963 TARGET SEEKING MISSILE 3 Sheets-Sheet 1 Filed Feb. 27,1962 INVENTOR.

NEWTON H. FISK Nov. 19, 1963 N. H. FISK 3,1

TARGET SEEKING MISSILE Filed Feb. 27, 1962 3 Sheets-Sheet 2 Nov. 19,1963 N. H. FISK TARGET SEEKING MISSILE 3 Sheets-Sheet 3 Filed Feb. 27,1962 United States Patent 3,111,088 TARGET SEEKING MISSHLE Newton H.Fisk, Orange County, Fla, assignor to Martin- Marietta Corporation,Middle River, Md, a corporation of Maryland Filed Feb. 27, 1962, Ser.No. 176,058 9 Claims. (Cl. 102-51) This invention relates to targetseeking missiles, and more particularly to radiant energy responsivetarget seeking missiles capable of detecting the presence and relativeposit-ion of a target and of altering course in flight as necessary tostrike the target or come within effective range thereof. Target seekingmissiles such as bombs, rockets, and the like, have been proposedheret0- fore comprising movable steering means such as rudders, vanes,or other air foils requiring linkages "and power actuators forpositioning thereof to effect deviations in trajectory in response tosignals from control means such as radiant energy responsive targetscanning apparatus operating independently of the steering means. Whilesuch systems have achieved a certain degree of refinement, there remainproblems relating to the provision of linkages and actuators which aresmall in size and light in weight and yet sufliciently powerful andreliable to accurately and rapidly posit-ion rudders and the likeagainst the resistance of air at high speeds. Additionally, such systemshave required relatively complex means for scanning the area ahead ofthe missile and for translating the relative position of the target intosignals for operating the rudder positioning means.

-It is a primary object of this invention to overcome the foregoingdisadvantages and shortcomings by providing an improved radiant energyresponsive missile and guidance system wherein target scanning andmissile steering or attitude control means are integrated to provide aparticularly simple, compact and reliable system.

Another object of this invention is the provision of a target seekingmissile and guidance system which is capable of looking on a targetwhich is off the missile axis, and of continuously applying a coursecorrecting force until the missile axis is brought into alignment withthe target.

As another object this invention aims to provide an improved targetseeking missile, such as a rocket powered explosive weapon or the like,to be propelled through the air toward an objective or target which maybe distinguished from its surroundings by radiation such asultra-violet, infra-red, or light energy reflected from or emanated bythe target, the missile being of a canard configuration having anelongated body or airframe comprising forward and after sectionsindependently rotatable in opposite directions about the longitudinalaxis of the missile, one of the sections, for example the after section,having fin means which impose a rotational moment thereon in onedirection of rotation with respect to a fixed frame of inertialreference, the other or forward section having cauards or other airfoils for imposing a rotative moment thereon in the opposite directionand for creating :a net lift normal to the missile axis and constant indirection with respect to the forward section, so that when the latteris freely rotating the effect of the not lift is simply to impose asmall oscillatory motion on the missile in its trajectory, and targetposition responsive means for actuating brake means between the sectionsfor causing the rotation of the forward section to be overcome by therotation of the after section and pass through a condition of zerorotational velocity with respect to the fixed frame of reference,whereby the net lift acts to efiect a deviation in the flight path ofthe missile in the form of a change of course or direction of traveltoward a target.

Another object of this invention is the provision of a target seekingmissile of the foregoing character wherein the forward section comprisesoptical means including an aperture rotatable therewith for scanning thetarget area and for causing an image of a target to fall on radiantenergy sensitive means, such as a photomultiplier tube in the aftersection, when the target is off the longitudinal axis of the missile,the photomultiplier tube being responsive to presence of light energy inthe form of the target image to send an electrical signal throughsuitable amplifying and rectifying means to actuate the brake meanswhich preferably comprises an electrically energized magnetic particlebrake. The aperture is so disposed with respect to the canard means thatthe target image falls on the photomultiplier tube and actuates thebrake to cause the forward section to reverse direction and pass throughzero rotational velocity with respect to the fixed frame of referencewhen the net lift or lateral effort of the canard means is acting on themissile in a direction tending to bring the missile axis towardalignment with the target.

The reverse rotation of the forward section and oper ture through asmall degree will cause the target image to be intercepted and theresulting loss of light energy on the photomultiplier tube to interruptthe brake energizing signal so that the forward section is caused by itscanard fins to again reverse and rotate through a small degree until theaperture once more allows the target image light energy to fall on thephotomultiplier tube and a signal to be passed to energize the brake andrepeat the reversing sequence of the forward section. Since theforegoing sequence of events results in rapidly changing rotativedirection or oscillation of the forward section within a small incrementof rotation, the net of the canard means will provide a lateral efiortwhich substantially constantly urges the missile to assume a course inalignment with the target. Thus, missiles embodying this invention maybe said to lock on the target. in one practical embodiment the canardmeans comprises four vanes or canards extending from the forward sectionat intervals, and three of which are oriented to provide the rotatingmovement which is utilized in scanning while.

the fourth is of reverse hand and cooperates with the canard oppositethereto to produce the net lift or lateral effort utilized for steeringthe missile.

Other objects and advantages of this invention will become apparent fromthe following detailed description of a preferred embodiment thereofread in conjunction with the accompanying sheets of drawings forming apart of this specification, and in which FIG. 1 is a side elevationalview of a rocket powered target seeking missile embodying the invention;

FIG. 2 is an enlarged front view of the missile of FIG. I viewed alongline 2--2 thereof;

FIG. 3 is a tail view of the missile taken along line 3-3 of FIG. 1;

FIG. 4 is an enlarged view of the missile, partly in section and withthe mid portion broken out;

FIGS. 5A through 5E are a series of schematic illustrations showingdifferent phases of operation of the inventiOn;

FIG. 6 is a schematic illustration showing the circuit missile isresponsive to light energy in the infra-red band of the spectrum such asmay be emanated or reflected from a target such as an armored vehicle ortank. Of course, missiles embodying the invention may be responsive toother forms of radiant energy such as ultraviolet, electrom-agnetic, orthe like either reflected from or emanated by a target or objective innon-radiating surroundings.

The missile 10 comprises an elongated airframe or body including anafter section 11 and a coaxial nose or forward section 12 which areindependently rotatable in opposite directions about the longtiudinalaxis of the missile. The after section 11 has a plurability of missilestabilizing tail fins 13 mounted thereon, there being four fins in thisinstance spaced at 90 intervals. The trailing edge of each fin 13 isbent as at 13a to provide a rolling moment to the after section of themissile airframe as it passes through the air in flight. This momentproduces clockwise rotation of the after section of the missile asviewed in FIG. 2 and with respect to a fixed frame of inertialreference. This missile 10 is adapted to be propelled by a conventionalrocket motor carried in airframe after section 11 and having a nozzle14- which opens through the tail end of the missile as shown in FIG. 3.

Missile 10 may be considered to be of basic canard configuration withthe fins 13 serving as wings and steering being effected by four canards16a, 16b, 16c, and 16d extending from, and forming part of, therotatable forward airframe section 12. Three of the canards, 16a, 16b,and Ida are oriented to provide a rotational moment, indicated by arrows17, to forward section. 12 as the missile passes through the air, whichmoment tends to effect rotation of the forward section in acounterclockwise direction as viewed from the nose in FIG. 2, and withrespect to the fixed frame of reference. Canard 16d, however, is of thereverse hand and cooperates with canard 16b opposite thereto to providea net lift or lateral eifort on the forward section of the missile asshown by vector arrows 18. The after section 11 is characterized bygreater rotational inertia than is the forward section 12 and therotational moment imposed on the after section by fins 13 is somewhatgreater than the oppositely directed rotational moment imposed on theforward section by canards 16a, 16b, and 16c.

It will be recognized that the net lift or lateral effort 18 issubstantially normal to the longitudinal axis of the missile and isconstant in direction with respect to the rotatatable forward airframesection 12. That is to say, the direction of the lateral effort rotateswith the forward section. This lateral effort is utilized in a mannerwhich will become apparent as the description proceeds to cause themissile to be accelerated from its normal trajectory and to curve towarda target.

Canards 16 are preferably formed of molded plastic material formedintegrally with a reflector member 21 presenting an annular, forwardlydirected parabolic reflecting surface 21 surrounding a recess a. Asshown in FIG. 4, reflector member 24) is supported for rotation aboutthe longtiudinal axis of the missile by ball bearing means, of which theouter race 23 is conveniently partially imbedded in the reflector memberand the inner race 24 is carried on an annular boss 25 defining acentral opening 26 in an end wall 27 after missile section 11.

Outer race 23 has a ring gear 36 formed thereon which is in meshingengagement with a pinion 31 fixed on the common shaft 32 of a magneticparticle brake 33 and a permanent magnet electric generator 34 mountedbehind wall 27 in after section 11. Rotation of forward section 12effects operation of permanent magnet generator 34- through pinion 31and shaft 32, while brake 33 is adapted to be energized to impede orhalt rotation of the forward section with respect to the rafter section11. Brake 33 and generator 34 form part of a missile steering controlcircuit including a radiant energy sensitive element such as aphoto-multiplier tube 35 mounted in alignment with opening 26, andadapted to convert radiant energy from a target into electrical signalsfor controlling brake 33 so as to effect steering of the missile towardthe target. Magnetic particle brake 33 is conveniently of a type definedas Model 3547A manufactured by Lear, Incorporated of Santa Monica,California, though other forms of electrically energized braking meansmay be used.

A dome 44 which is transparent to infra-red light energ, is secured toreflector member 2%} and supports a second reflector member 41 having areflecting surface 42 facing reflecting surface 21. Reflecting surfaces21 and 42 are coaxial with the longitudinal axis of missile 1t) and withopening 26 in wall 27 of after section 11. A wedge shaped aperture 43,including an angle of about 40, is formed in reflector member 20 betweenrecess 26:: thereof and opening 26, the apex of the aperture terminatingshort of the longtiudinal axis of the missile as is best shown in FIGS.5A-5E. Aperture 43 is disposed at approximately from the lift producingcanard 16d and extends away from the missile axis in a directionopposite to the net lift vector 18. Preferably, the aperture is providedwith a suitable infra-red filter 44.

Reflecting surfaces 21 and 42 are arranged to gather radiant energyphotons or rays from a field of view of 15 from the missile axis tofocus the energy rays toward photomultiplier tube 35. When the forwardsection 12 is rotating in flight, aperture 43 rotates therewith andcauses the target area to be scanned and an image I of target T, whichis off the missile axis but within the field of view, is formed onphotomultiplier tube 35 as shown in FIG. 4. It should here be noted thatin the present example the image is formed on the opposite side of themissile axis from that occupied by the target T, because of thereflective principle used.

Photomultiplier tube 35, which may be tube type IP28 such as ismanufactured by the Radio Corporation of America, is capable of varyingelectron flow between cathode and anode means in accordance with theintensity of light energy falling on the tube. Thus, photomultipliertube 35 may be said to convert photons or light energy into an amplifiedelectrical signal. The anode means are impressed with a suitableelectrical potential by means of a battery 47 and a suitable powersupply as as is best shown in FIG. 6. Battery 47 is preferably asilver-zinc type such as is manufactured by the Eagle- Picher Company ofCincinnati, Ohio, while the power supply 48 is preferably a conventionalDC. to A.C. inverter of the transistor oscillator type, including A.C.voltage step-up means, the power supply being comparable to thatidentified as Model 591H-C of Arnold Magnetic Corporation of LosAngeles, California. Photornultiplier tube 35 is connected to pass itsoutput signals through a band pass filter 49, these signals beingapplied as one of two inputs to a conventional transistor amplifier 50which is in turn connected through rectifier 51 to brake 33.

The band pass filter 49' and amplifier 50 may be of any types suited tothe signal frequencies concerned, and in the present embodimentamplifier 50 is similar to type 466A made by Hewlett-Packard Company ofPalo Alto, California. Rectifier 51 is preferably a silicon diodesemiconductor type 1N599.

The foregoing components have been found to fulfill the requiredfunctions in the embodiment being described, although other comparablecomponents, well known to those skilled in the art to which theinvention pertains, may be used in practicing the invention. The battery47, power supply 48, band pass filter 49, amplifier 50, and rectifier 51are conveniently assembled in an annular package 52 mounted in aftersection 11.

The application of light energy to photomultiplier tube 35, such as byformation of an image I thereon, causes the tube to pass a signalthrough filter 49 to amplifier 50, which signal is there amplified bypower received from 5. battery 47. The amplified signal is passedthrough rectifier 51 for conversion to direct current which is utilizedto energize magnetic particle brake 33. Brake 33 is there by actuated tooppose rotation of forward section 12 with respect to after section 11so long as light energy, such as image I, remains focused on thephotomultiplier tube.

Conversely, whenever little or no light of the wavelength concernedfalls on photomultiplier tube 35, such as when aperture 43 is notpositioned in alignment with image I, there is no signal passing fromthe photomultiplier tube through amplifier 50 and rectifier 51 to brake33. In this condition the forward section is allowed to rotate under theinfluence of canards 16a, 16b, and 160 in one direction with respect tothe inertial reference frame, while the after section 11 is rotating inthe opposite direction under the influence of fins 13.

The rate of scanning rotation by forward section 12 is limited byapplying the electrical output of permanent magnet generator 34, whichis proportional to the angular velocity of shaft 32, as a second inputsignal to amplifier 50 Where it is amplified and then transmitted tobrake 33 through rectifier 51. It will be recognized that the effect ofgenerator 34 is to cause brake 33 to dampen the rotational moment offorward section 12, this being desirable to stabilize the seekingcharacteristics of the missile. In the present example, the aftersection 11 has a steady roll rate of about 15 radians per second in aclockwise direction as the missile is viewed in FIG. 2, while the steadystate roll rate of the lighter forward section is limited by thedampening effect of generator 34 to about 32 radians per second in theopposite direction.

Because of the greater rotational inertia of the after section and thelarge rotational moment of fins 13, energization of brake 33 to opposerotation of forward section 12 with respect to after section 11 inresponse to formation of a target image on photomultiplier tube 35, willresult in the rotation of the forward section being overcome by rotationof the after section so that the forward section passes from its normalcounterclockwise rotation through zero rotational velocity with respectto the fixed inertial frame of reference and into clockwise rotationwith the after section.

Referring to FIGS. A through SE, in which the reflector member 20 andaperture 43 are viewed from a position forward of the missile andlooking aft toward the nose thereof, the sequence of events in targetacquisition and steering will be described. In FIG. 5A forward section12 is rotating counterclockwise under the influence of canards 16a, 16b,and 16c, so that the optical system including aperture 43 is scanning anarea ahead of the missile. At this time a target, to the right of themissile axis as viewed in FIG. 5A, is represented by a radiant energyimage I intercepted by member 20 which prevents the image energy fromreaching the photomultiplier tube 35.

As aperture 43 rotates to the FIG. 5B position, the image I is formed onthe photomultiplier tube so as to fully energize brake 33. Energizationof brake 33 in response to the formation of the target image onphotomultiplier tube 35 halts rotation of the forward section 11 withrespect to the after section and, because of the greater rotationalinertia of the after section and the large rotational moment of fins 13,the forward section will pass from its counterclockwise rotatingcondition through zero rotational velocity with respect to the fixedinertial frame of reference and into clockwise rotation with the aftersection. The finite inertia of the forward section requires some time(on the order of .01 second) for the brake 33 to reverse rotation of theforward section and during this time the image I is brought deeper intothe sensitive area defined by aperture 43 as shown in the brake on viewof FIG. 5B.

Thereafter, the forward section 12 and aperture 43 will rotate clockwisewith after section 11 for a few degrees until the image I is interceptedby member 20 and the light energy thereof is lost to photomultipliertube 35 as shown in FIG. 5C. The result of loss of light energy on thetube 35 is that the signal ceases to pass therefrom through filter 49,amplifier 50, and rectifier 51 to brake 33, and the forward section isreleased to resume its counterclockwise rotation under the influence ofcanards 16a, 16b, and 160. Again, the forward section passes throughzero rotational velocity as it reverses from clockwise tocounterclockwise rotation. This counterclockwise rotation of forwardsection 12 will continue only for a few degrees until the image I isregained as shown in the subsequent brake on view of FIG. 5D at whichtime the rotation is again reversed.

The forward section 12 is thereby oscillated between clockwise andcounterclockwise rotation, with the amplitude of oscillation beinglimited to a few degrees between zero rotational positions with respectto the fixed inertial frame of reference. Because of the positionalrelationship of the aperture 43 to canards 16b and 16d, the net liftproduced thereby exerts a lateral effort 18 which acts throughout theperiod of oscillation to veer the missile to a course more directlytoward the target T.

The relative movement path of image I with respect to forward sectionmember 20 and aperture 43 is represented by a dotted line 53 in FIGS.5A5E, by which it may be seen that the image moves progressively towardthe center of member 20 as the longitudinal axis of the missile 10 isbrought into alignment with the target.

When image I reaches the FIG. 5B position, the missile is on target andthe image is occluded because of the blunted shape of the aperture 43.The occlusion of the image interrupts the photomultiplier output signaland brake 33 releases the forward section 12 for scanning rotation whichcontinues until the target is hit or the image moves out of the FIG. 5Eposition because of target movement, windage, or the like, in which casethe steering sequence will be resumed as necessary to return the missileto an on target course.

It will be recognized that although the forward section 12 and thedirection of canard net lift or lateral efiort 18 oscillate slightlyduring the seeking or steering phase, the resulting effect is that themissile is locked on the target and the major force components of thenet lift act continuously to veer the missile 10 toward alignment withthe target.

The steering characteristics of the missile 10 may be altered bymodifying the leading edge of the aperture 43 to provide proportionalcontrol of the brake means. For example, if it is desired to reduce theoscillation of for: ward section 12 to effect a still more constantforce for veering of the missile toward an on target course, theaperture may be modified by providing the leading edge thereof withshading means 55 as shown in FIG. 7. The shading means 55 issubstantially opaque at 55a to the radiant energy concerned and becomesgradually more transparent thereto going towards edge 55b.

When the target image is acquired in the lightly shaded or open portionof the aperture 43-, the brake will be applied as before, causing theforward section 12 to roll with the after section and the image I toprogress into the deeper shaded portion of the aperture. The intensityof the radiant energy reaching the photomultiplier tube 35 will bereduced until brake 33 is allowed to slip at a rate which will maintainthe image I under a substantially constant degree of shading. This, ofcourse, will maintain the forward section 12 so that the net lift willbe continuously and fully acting to direct the Thissile toward thetarget. The image I will therefore follow the more direct relativemovement path shown in FIG. 7 until it reaches the occluded centralportion of the reflector 20 corresponding to the longitudinal axis ofthe missile, at which time scanning will 'be resumed.

Other modifications of aperture 43 may be made to achieve differentflight characteristics, for example the shape of the leading edge couldbe curved to provide increasing or decreasing amounts of course changesas the target image approaches the center.

From the foregoing description it will be apparent that both thescanning function and the steering function are effected by use of thecanard means 15, and that this integration of functions eliminates thenecessity of providing and operating independent rudders, impulse means,or the like. It will also be apparent that missiles embodying theinvention may be made responsive to other forms of energy such asvisible light, ultraviolet, or sound waves, and that other forms ofbraking means, canards, and energy focusing elements, than thosedescribed, may be used.

Accordingly, although the invention has been described in considerabledetail, and with reference to a specific target seeking missileembodying the invention, it will be understood that the invention is notlimited thereto, but rather the invention includes all thosemodifications, adaptations, substitutions, and uses as are reasonablyembraced by the scope of the claims hereof.

Having described my invention, I claim:

1. A target seeking missile comprising:

(a) an elongated airframe having first and second coaxial sectionsrotatable relative to one another about the longitudinal axis of theairframe,

(b) first fin means on said first section for effecting rotation thereofin one direction about said axis and for imposing a net lift normal tosaid axis and acting in a direction which is rotatable with said firstsection,

(c) second fin means on said second section for effecting rotationthereof in a direction opposite to said one direction,

(a?) brake means between said sections and actuable to oppose relativerotation of said sections,

(e) said rotation of said second section being effective to overcomesaid rotation of said first section upon actuation of said brake meansso that said first section passes through a condition of zero rotationalvelocity and undergoes a reversal of rotative direction,

(f) radiant energy sensitive means adapted to produce a brake actuatingsignal corresponding to energy falling thereon,

and

(g) scanning means in one of said sections for causing radiant energyfrom a target which is off said axis to fall on said sensitive means andactuate said brake means only when said net lift is acting in thedirection in which said target is off said axis.

2. A target seeking missile as defined in claim 1 and wherein saidscanning means comprises aperture means rotatable with said one sectionso that said reversal of rotative direction of said first sectioninterrupts said energy falling on said sensitive means, and said brakemeans is alternately actuated and released to repeatedly reverserotative direction of said first section so that said net lift providescontinuous lateral effort for veering said missile toward said target.

3. A target seeking missile comprising:

(a) an elongated airframe having forward and after coaxial sectionsrotatable relative to one another about the longitudinal axis of theairframe,

(b) canard means on said [first section for effecting rotation thereofin one direction about said axis and for imposing a net lift normal tosaid axis and acting in a direction which is rotatable with said forwardsection,

() fin means on said after section for effecting rotation thereof in adirection opposite to said one direction,

(d) brake means between said sections and actuable to oppose relativerotation of said sections,

(2) said rotation of said after section being effective to overcome saidrotation of said forward section upon actuation of said brake means sothat said forward section passes through a condition of zero rotationalvelocity,

(1) radiant energy sensitive means mounted in said airframe and adaptedto produce a brake actuating signal corresponding to energy fallingthereon,

and

g) scanning means in said forward section for causing radiant energyfrom a target which is off said axis to fall on said sensitive means andactuate said brake means only when said net lift is acting in thedirection in which said target is off said axis.

4. A missile as defined in claim 3 wherein said canard means comprises aplurality of air foils distributed about said forward section, amajority of said air foils being of like hand so as to effect saidrotation and at least one of said air foils being of reverse hand andcooperable with one of said majority to produce said lateral effort.

5. A target seeking missile =as defined in claim 3 and wherein saidscanning means comprises aperture means rotatable with said one sectionso that said reversal of rotative direction of said first sectioninterrupts said energy falling on said sensitive means, and said brakemeans is alternately actuated and released to repeatedly reverserotative direction of said first section so that said not lift providescontinuous lateral effort for veering said missile toward said target.

6. A target seeking missile as defined in claim 5 and wherein saidaperture means comprises energy shading means of graduated transparencywhereby said brake means allows said forward section to rotate asnecessary to maintain an image of predetermined intensity on saidsensitive means and to maintain said lateral effort acting toward saidtarget.

7. A target seeking missile comprising:

(a) an elongated airframe having an after section and a forward sectionrotatable relative thereto about the longitudinal axis of said airframe,

(b) stabilizer means on said after section for producing missile roll inone direction about said axis,

(0) canard means comprising a plurality of air foils distributed aboutsaid forward section,

(d) a majority of said air foils being of like hand for effectingrotation of said forward section opposite to said roll,

(2) at least one of said air foils being of reverse hand and cooperablewith one of said majority to produce a lateral effort normal to saidaxis and constant in direction with respect to said forward section,

(1) radiant energy sensitive means in said after section,

(g) said rotatable forward section comprising optical scanning means forfocusing a radiant energy image of a target which is off said axis, withsaid image having a position off said axis in a direction determined bythe position of said target,

(it) said scanning means comprising an aperture ro tatable with saidforward section and disposed on one side of said axis in a predeterminedposition so as to pass said image to said sensitive means only when saidlateral elfort is acting in said target direction,

and

(i) brake means between said forward and after sections and responsiveto the presence of said image on said energy sensitive means to opposerotation of said forward section with respect to said after sectionwhereby rotation of said forward section is overcome by said aftersection and said lateral effort acts to veer said missile toward saidtarget.

8. A target seeking missile as defined in claim 7 and wherein saidaperture means comprises image shading means having graduatedtransparency, said shading means being adapted to increase and decreasethe image intensity so as to change the effect of said braking means totend to maintain said fori ivard seciion yvit zh said lateral ReferencesCited in file of this patent gliiolrtt ;;:tt111nsgaie5 rg1;1g1;ct ns1yto veer said missile into alrgn- UNITED STATES PATENTS 9. A tar-getseeking missile as defined in claim 7 and 2,911,167 Null et a1 1959wherein said canard means comprises four air foils and 5 said majoritycomprises three air foils of like hand.

1. A TARGET SEEKING MISSILE COMPRISING: (A) AN ELONGATED AIRFRAME HAVINGFIRST AND SECOND COAXIAL SECTIONS ROTATABLE RELATIVE TO ONE ANOTHERABOUT THE LONGITUDINAL AXIS OF THE AIRFRAME, (B) FIRST FIN MEANS ON SAIDFIRST SECTION FOR EFFECTING ROTATION THEREOF IN ONE DIRECTION ABOUT SAIDAXIS AND FOR IMPOSING A NET LIFT NORMAL TO SAID AXIS AND ACTING IN ADIRECTION WHICH IS ROTATABLE WITH SAID FIRST SECTION, (C) SECOND FINMEANS ON SAID SECOND SECTION FOR EFFECTING ROTATION THEREOF IN ADIRECTION OPPOSITE TO SAID ONE DIRECTION, (D) BRAKE MEANS BETWEEN SAIDSECTIONS AND ACTUABLE TO OPPOSE RELATIVE ROTATION OF SAID SECTIONS, (E)SAID ROTATION OF SAID SECOND SECTION BEING EFFECTIVE TO OVERCOME SAIDROTATION OF SAID FIRST SECTION UPON ACTUATION OF SAID BRAKE MEANS SOTHAT SAID FIRST SECTION PASSES THROUGH A CONDITION OF ZERO ROTATIONALVELOCITY AND UNDERGOES A REVERSAL OF ROTATIVE DIRECTION, (F) RADIANTENERGY SENSITIVE MEANS ADAPTED TO PRODUCE A BRAKE ACTUATING SIGNALCORRESPONDING TO ENERGY FALLING THEREON, AND (G) SCANNING MEANS IN ONEOF SAID SECTIONS FOR CAUSING RADIANT ENERGY FROM A TARGET WHICH IS OFFSAID AXIS TO FALL ON SAID SENSITIVE MEANS AND ACTUATE SAID BRAKE MEANSONLY WHEN SAID NET LIFT IS ACTING IN THE DIRECTION IN WHICH SAID TARGETIS OFF SAID AXIS.